1. Field of the Invention
This invention relates generally to a secondary fuel system for diesel engines. More particularly, but not by way of limitation, this invention relates to a system for delivering a gaseous fuel such as propane or natural gas into the intake air of a diesel engine.
2. Brief Description of the Related Art
It is well known in the art that the injection of gaseous fuel such as propane into the intake air of a diesel engine has several benefits. For a given work output of a diesel engine, the injection of propane reduces the amount of diesel fuel required. Similarly, for a given consumption of diesel fuel, the injection of propane increases the work output of the engine. Propane also promotes more complete combustion of diesel fuel, reducing the amount of pollutants emitted from the engine.
The prior art known to the applicant attempts to provide systems for injecting gaseous fuel into the air intake of a diesel engine at automatically varied rates. These systems inject the fuel at a rate that is automatically adjusted in response to one or more measurements such as exhaust temperature, flowrate of intake air, engine RPM, or the like. In addition, systems have been developed for turbo-charged diesel engines which adjust the amount of gaseous fuel injected in response to “boost” pressure created by the turbo-charger. These prior art systems adjust the amount of gaseous fuel injected by complex mechanical and electrical means. The automatic adjustment of these systems requires complex components and controllers, each of which are susceptible to failure.
For example, U.S. Pat. No. 6,422,015 describes a system using a progressive valve activated by turbo boost pressure. The mechanism injects an increasing amount of propane as the boost pressure increases. The system utilizes a spring and diaphragm in its automatically adjusting valve. The system is thus subject to failure due to constant stresses and the limited life of the diaphragm. Further, the system may be subject to inconsistent performance due to the effects of temperature changes on the elasticity of the diaphragm.
Many diesel engines are designed to operate at a constant engine load and corresponding constant work output. The prior art systems are designed to operate on diesel engines of varying output and are much more complex than necessary for engines that run under substantially static conditions. The additional complexity of the prior art systems reduces their reliability and needlessly increases the expense of a system for a constant-output engine. Thus, a need exists for a gaseous fuel injection system suited for diesel engines that operate under substantially constant conditions. More specifically, but not by way of limitation, a need exists for a gaseous fuel injection system of simpler construction with subsequent increased reliability and decreased cost.